This application claims the benefit of Korean Application No. 2000-79734, filed Dec. 21, 2000, in the Korean Industrial Property Office, the disclosure of which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to a method and apparatus to generate a monitoring signal for an optical recording/reproducing system to monitor the state of the optical recording/reproducing system and to adjust the optical recording/reproducing system to an optimal state.
2. Description of the Related Art
Generally, at an initial state optical recording/reproducing systems are adjusted to an optimal state with respect to a radial tilt, tangential tilt, defocus and detrack. In order to adjust an initial system state, conventionally, an envelope signal of a radio frequency (RF) signal is used, which is the sum of signals output from an information signal recording/reproducing photodetector with a plurality of separate plates.
However, since a high density optical disc, such as a next generation DVD in the process of development and called a high-definition digital versatile disc (HD-DVD), has a relatively very small track pitch with respect to the size of an optical spot compared to a CD or DVD, a crosstalk component is mixed into the RF signal due to an adjacent track. Accordingly, it is difficult to detect the envelope of the RF signal.
FIGS. 1A through 1C illustrate changes in an RF signal according to changes in an optical spot and track pitch and show an RF signal at a track pitch Tp of 0.74 xcexcm (in the case of a DVD), 0.46 xcexcm and 0.37 xcexcm, respectively. The RF signal shown in FIGS. 1A through 1C was detected using light having a wavelength of 400 nm and an objective lens having a numerical aperture of 0.6. Here, a high density optical disc such as a next generation DVD (for example, a HD-DVD) will have a track pitch no greater than about 0.37 xcexcm.
As is evident from FIGS. 1A through 1C, when a track pitch decreases with respect to an optical spot with a predetermined size, a crosstalk component mixed into an RF signal increases. As a result, the RF signal is degraded, and it becomes difficult to detect the envelope of the RF signal.
Accordingly, it is difficult to adjust an optical recording/reproducing system to an optimal initial state based on the envelope of an RF signal with a high density optical disc having a small track pitch with respect to an optical spot.
To solve the above problems, it is an object of the present invention to provide a method and apparatus to generate a monitoring signal for an optical recording/reproducing system to adjust the initial state of an optical recording/reproducing system to an optimal state even with respect to a high density optical disc having a small track pitch with respect to an optical spot.
Additional objects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.
Accordingly, to achieve the above and other objects of the invention, there is provided a method of generating an optical recording/reproducing system monitoring signal, by dividing at least part of a light beam reflected from a recording surface of a recording medium into first through fourth light areas in directions corresponding to radial and tangential directions of the recording medium, the first through fourth light areas being ordered counterclockwise or clockwise, outputting first through fourth detection signals from the first through fourth light areas, detecting a phase difference between a first sum signal obtained by summing the first and third detection signals and a second sum signal obtained by summing the second and fourth detection signals, outputting first and second phase difference signals based upon the detected phase difference, and summing the first and second phase difference signals to generate an optical recording/reproducing system monitoring signal.
Preferably, the method further includes low-pass filtering the first and second phase difference signals before summing.
To achieve the above and other objects of the invention, there is also provided an apparatus to generate an optical recording/reproducing system monitoring signal, including a photodetector including first through fourth light receiving areas for dividing at least part of a light beam reflected from a recording surface of a recording medium into first through fourth light areas in directions corresponding to radial and tangential directions of the recording medium, the first through fourth light areas being ordered counterclockwise or clockwise, a phase difference detector to compare a phase of a first sum signal obtained by summing first and third detection signals output from the first and third light receiving areas, respectively, with a phase of a second sum signal obtained by summing second and fourth detection signals output from the second and fourth light receiving areas to output first and second phase difference signals; and an adder to sum the first and second phase difference signals output from the phase difference detector to generate an optical recording/reproducing system monitoring signal.
Preferably, the apparatus further includes a low-pass filter to low-pass filter the first and second phase difference signals between an output terminal of the phase difference detector and an input terminal of the adder.
The first through fourth light receiving areas may be spaced out in at least one direction between the directions corresponding to the radial and tangential directions.